In this article, Special Educational Needs Coordinators' (SENCOs) boundary work in Swedish upper-secondary school is examined in comparison with similar special education professionals in a Nordic context. Here, boundary work is understood as SENCOs' attempts to shape and influence boundaries, distinctions and demarcations between agents and between and within in-school settings. The empirical material was generated through semi-structured lifeworld interviews and open-ended diaries collected from nine SENCOs. The design of the study is lifeworld phenomenological according to the Gothenburg tradition, the analysis is hermeneutical. The results show that SENCOs' boundary work consists of continuous processes that are in constant states of becoming. The boundary work is interwoven with SENCOs' agency, especially while acting as agents of change. Moreover, various understandings of inclusion seem to create tensions, thereby making boundary work central for SENCOs' ability to mitigate said tensions between agents in school. These results corroborate previous claims of inclusion as an ambiguous concept. Finally, we ask whether it would be possible and constructive to understand inclusion as a boundary object. A boundary object is sufficiently plastic to retain an identity while still being sufficiently modifiable to suit several standpoints, potentially enabling cooperation without a consensus regarding the definition of inclusion.